This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Tubular strings are inserted into and pulled from wellbores (e.g., boreholes) at various times during the life of a well for various purposes. For example, tubular strings (e.g., drill pipe) are assembled and run into the well for drilling the wellbore, to line the wellbore (e.g., casing, liners, screens, etc.), and to position tools (e.g., tubing, etc.) in the wellbore.
A rig is typically employed to assemble the tubular string for insertion into the wellbore and to dissemble the tubular string as it is pulled from the wellbore. Generally, a rig floor mounted support device, e.g., a gripping spider, supports a first tubular (e.g., casing) that extends into the wellbore. A single joint elevator may be utilized to hoist the add-on tubular segment and align it with the first tubular. The add-on tubular segment is then connected (e.g., made-up) to the first tubular to form a tubular string. Threaded tubulars may be made-up by various tools including, but not limited to, power tongs, spinners, and top drives. A vertically movable support device, e.g., string elevator, top drive quill, or tubular running tool, engages the add-on tubular to support the tubular string. The floor mounted support device, e.g., spider, then disengages the tubular string and the tubular string is lowered therethrough to a desired position. The floor mounted support device, e.g., spider, then re-engages the tubular string and the vertically movable support device, e.g., string elevator, disengages the tubular string. The sequence may be reversed when pulling the tubular string from the wellbore and disassembling the tubular string.
Various safety systems have been utilized to ensure or promote assurance that at least one of the floor mounted tubular support device and a vertically moveable tubular support device (e.g., elevator) is in engagement with a tubular segment before the other tubular support device is permitted to release its load supporting engagement of the tubular. For example, interlock systems such as the grip assurance systems disclosed in U.S. Pat. Nos. 4,676,312, 5,791,410 and 5,909,763, which are incorporated herein by reference, have been provided to ensure that at least one tubular support device is engaged with the tubular string before the other tubular support device is disengaged from the tubular. However, heretofore an interlock system has not been provided that prevents opening a tubular support device in response to sensing a load acting on the tubular support device.